Loop antenna



w. BERNDT 2,202,368

} LOOP ANTENNA Filed Nov. 11, 1937 May 28, 1940. I

INVENTOR WAL TER a IQ/V07 ATTORN EY ill ' shielding means or with thecasing R, the an tenna effect may be cut down to a very low value.

Patented May 28, 1940 LOOP ANTENNA Walter Berndt, Berlin, Germany,assignor to Telefunken Gesellschaft fiir .Drahtlose Telegraphic in. b.11., Berlin, Germany, a corporation of Germany Application November 11,1937, Serial No. 173,992 In Germany October}, 1936 t 5'Claims.- (01.250-33) 1 This invention relates to a frame or loop antenna arrangementpossessing only a small antenna effect.

It is known in the art that the direction diagrams or characteristics ofloops or frames correspond to the calculated values only when it ispossible to eliminate the antenna effect of the loop. Several ways andmeans have been disclosed in the earlier art to this end. The loop andthe input circuit may be built symmetrically. The loop may be shieldedelectrically; the leads brought-to the loop maybe grounded throughdifierential condensers, while the antenna effect I finally may becompensated by an auxiliary antenna. Yet, in spite of all these steps anappreciable antenna effect will be found to be present, and it willalways be compensated by the last-named means, namely, an auxiliaryantenna. The requisite auxiliary antenna must possess a certainefiective minimum size if its action is to be attainable in an adequatemeasure. ever, it is often undesirable or inconvenient to use a largeauxiliary antenna. For this reason it is desirable to design a loopantenna having inherently a low antenna effect.

The antenna effect" of a loop of known construction is essentially dueto capacitive dissymmetries to ground or casing of the two halvesthereof. Another part of the antenna efiect is due to the leads broughtto the loop which, in most cases, are coupled with a circuit presentinga dissymmetric relation to ground.

Referring, now, to the drawing, Fig. 1 shows one form of my invention,while Figs. 2 and 3 show modifications thereof. I

According to this invention, therefore, a loop is used which is notfurnished with any direct supply leads or downleads and which consistsof one or several turns L closed upon themselves; The

connection with the receiver apparatus, as shown in Fig. 1, isestablished bymeans of a coil W annularly surrounding the turner theturnsof the loop. However, also two symmetrically mounted coils W, W maybe employed as shown in Fig. 2. By means of static shielding of theannular coil or coils as shown in more detail in Figure 3, andconnection with ground of the A further reduction in the antenna-effectis attainable by grounding the loop antenna L-or connecting it with thecasing R in a symmetrical manner. The grounding point of the loop turnswill then'be symmetrical to the annular coils (Fig, 2') or to theannular coil (Fig. 3).

- nular coil.

The, annular coils are included suitablyin a tuned circuit which actsupon the grid of ,a tube (Fig. 2). Ifas close a coupling as possible isto be insured between the loop and the grid circuit,

then the core of the annular coil may consist of.

iron or of a material containing low-loss iron K, asshown in Fig. 3.

By the use of two similar annular coils which.

are placedupon both sides of the grounding point of the loop, thelooparrangement is made of symmetric construction. 7 l

If the loop antenna is .used for pickingup a wide wave band, then itwill be expedientto; provide the annular coil with several convolutionswhich are tapped or reversed, it being understood, of course, that foreach wave band-distinct annularcoils could be employed.

To obtainspecial directional effects the loop antenna, of this invention'whichinheres no antenna effect at all or only a very small one,.

could be combined with one or several like or similar antennae; and thesame could then be used either for reception or for transmission.

Referring to Fig. 3, R. denotes the loop casing which acts also as ashield for the convolutions L and W the winding while S indicates ashield for the winding W. o By the ground terminal indicated at E, theconvolutions ofvthe loop are in referenceto .the an-' earthedsymmetrically I claim:

1. Loop antenna comprising convolutions, saidconvolutions being closedupon themselves to form a closed circuit, means for coupling said loopto a receiver comprising coils annularly surrounding the-loopconvolutions and means for shielding said loop convolutions including acasing surrounding said convolutions and connected to the convolutionsat the center of the portion surrounded by said coupling means.

2. A loop antenna comprising one or more con volutions said loopconvolutions beirig closed upon themselves to form aclosed circuit,means for coupling said loop to ,a receiver comprising a coil annularlysurrounding the loop convolutions and means for electrostaticallyshielding saidcoil surrounding said coil and connected to ground at apoint intermediate the ends thereof.

3. Loop antenna comprising convolutions, said convolutions being closedupon themselves to .form a closed, circuit, means for coupling said Iloop to a receiver comprising a coil annularly sur- I rounding the loopconvolutions and means for,

shielding said loop convolutions including a casing'surrounding saidconvolutions and connected to the convolutions at the center of theportion surrounded by said coupling means.

4. Loop antenna comprising a convolution, said convolution being closedupon itself, to form a closed circuit, means for coupling said loop to areceiver comprising coils annularly surrounding the loop convolution andmeans for shielding said loop convolution including a casing surroundingsaid convolution and connected to the convolution at the center of theportion surrounded by said coupling means.

5. Loop antenna comprising a convolution, said convolution being closedupon itself, to form a. closed circuit, means for coupling said loop toa receiver comprising a coil annularly surrounding the loop convolutionand means for shielding said loop convolution including a casingsurrounding said convolution and connected to the convolution at thecenter of the portion sur- WALTER BERNDT.

